The present invention relates generally to the field of manufacturing processes utilizing one or more process gases. More particularly, the present invention is directed to a system for and method of monitoring the flow of process gases from a gas delivery system during the manufacture of semiconductor devices to determine if the gas delivery system is properly calibrated.
The manufacture of microelectronic devices, such as semiconductor and superconductor devices, requires precise control of the amount of one or more gases used during processing of a wafer upon which the devices are formed. Wafer processing of this sort includes subjecting the wafer to processing steps such as film deposition, doping and etching. The concentration and/or amount of processing gas(es) present in a wafer processing chamber during wafer processing can affect one or more physical properties, such as film thickness, dopant concentration and depth of etch, among others, of the structure of the microelectronic devices that have small error tolerances that must not be exceeded to produce devices that function properly. In addition, precise control of the concentration and/or amount of process gas(es) is necessary to ensure uniformity among devices produced in different processing chambers or in the same chamber but at different times. For at least these reasons, precise control of the concentration and/or amount of the process gas(es) within the processing chamber during wafer processing is vital to manufacture of such devices.
The concentration of each process gas within a process chamber is typically controlled by controlling the rate of flow of the gas into the chamber using a flow regulator, such as a mass flow controller (MFC). The MFC must be highly accurate to achieve the precise concentration of gas required for a particular processing step. To ensure the accuracy of the MFC, it must be calibrated. Whenever an MFC is new or is being used in a processing system for the first time, it undergoes an initial calibration. Subsequent to initial calibration, the MFC is re-calibrated periodically to ensure it is operating within acceptable limits.
Re-calibration of an MFC is typically performed in-situ using a xe2x80x9crate-of-risexe2x80x9d test. The rate-of-rise test generally involves flowing a purge gas into the processing chamber, pumping the processing chamber to a base pressure and then flowing a gas through the MFC for a known period of time. Based upon the known volume of the processing chamber, the temperature of the test gas, the pressure change within the chamber and the elapsed time, an empirical flow rate through the MFC may be determined. The empirical flow rate may then be compared to the design flow rate. Typically, if the difference between the empirical and design flow rates is greater than about 10% of the design flow rate, the MFC is deemed defective and is removed from service.
A drawback of this method is that there are a number of factors that can lead to a false determination that the flow regulator is out of calibration. For example, the processing chamber isolation valve located downstream of the processing chamber and/or the chamber itself may leak. In addition, the volume of the processing chamber may be diminished from its original volume due to polymer buildup or other deposition buildup on the interior of the walls of the processing chamber. Another drawback of this method is that the processing system under re-calibration must be taken out of production to perform the test.
In one aspect, the present invention is directed to a fluid delivery system for supplying at least a first fluid to a processing chamber. The fluid delivery system comprises a first flow meter located upstream of and in fluid communication with the processing chamber. The first flow meter is for generating a first flow signal. A second flow meter is located upstream of and in fluid communication with the first flow meter. The second flow meter is for measuring the flow of the first fluid. The fluid delivery system further comprises a comparator containing a comparend. The comparator is operatively coupled to the first flow meter and is adapted for comparing the first flow signal to the comparend.
In another aspect, the present invention is directed to a method of monitoring flow within a processing system. The processing system has a processing chamber, a first flow meter located upstream of and in fluid communication with the processing chamber. A second flow meter is located upstream of and in fluid communication with the first flow meter. The second flow meter is for measuring the flow of a fluid. The method comprises the steps of sensing a first flow signal at the first flow meter and comparing the first flow signal to a comparend.